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 A171652 The initial decimal digits of 2^a(n) are the decimal digits of n followed by n. 2
 50, 51, 25, 145, 142, 119, 86, 239, 93, 1558, 1598, 761, 1183, 6651, 5515, 4183, 34, 8990, 1343, 4180, 7987, 10628, 938, 5519, 4177, 10213, 10326, 6652, 1327, 5516, 12326, 4184, 11964, 6928, 6649, 8991, 653, 10373, 11549, 4181, 3706, 7988, 5862, 10629, 8988, 939, 13084 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES E.I. Ignatjew, Mathematische Spielereien, Urania Verlag Leipzig-Jena-Berlin, 2. Auflage 1982 LINKS EXAMPLE a(1) = 50; 2^50 = 1125899906842624 a(2) = 51; 2^51 = 2251799813685248 a(3) = 25; 2^25 = 33554432 a(10) = 1558; 2^1558 = 10109583053...744 PROG (PARI) double(n, k)=n\=10^(#Str(n)-2*k); if(n%10^k==n\=10^k, n) a(n)=my(s=#Str(n)); for(k=1, 1e6, if(double(1<

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Last modified October 14 07:31 EDT 2019. Contains 327995 sequences. (Running on oeis4.)